1. Field of the Invention
The present invention relates to a sensor equipped wheel support bearing assembly having incorporated therein a sensor for detecting a load imposed on a bearing area of a vehicle wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the wheel support bearing assembly equipped with a sensor for detecting the rotational speed of one of automotive wheels has hitherto been well known in the art. While the automobile traveling safety precaution is hitherto generally taken by detecting the rotational speed of wheels, it is not sufficient with only the rotational speed of the wheels and, therefore, it is required to achieve a control for safety purpose with the use of other sensor signals.
In view of this, it may be contemplated to achieve an attitude control based on a load acting on each of wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking, and, thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheel tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads, so that the attitude control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of the front wheel diving during the braking, and prevention of the vehicle wheels diving brought about by an uneven distribution of live loads) can be accomplished. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Also, in the event in the near future the steer-by-wire is introduced and the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, is increasingly used, information on the road surface comes to be required to transmit to the steering wheel hold by a driver by detecting a wheel axis direction load.
In order to meet those needs hitherto recognized, the wheel support bearing assembly has come to be suggested, in which a strain gauge is applied to to an outer ring of the wheel support bearing assembly so as to detect the strain. (See, for example, the Published International Application WO01/077634).
The outer ring of the wheel support bearing assembly is a bearing component part, which has raceway surfaces and is required to have a strength and which is manufactured through complicated process steps including, for example, plastically deforming, turning, heat treatment and grinding. For this reason, where the strain gauge is affixed to the outer ring such as disclosed in the above mentioned published patent document, there are problems in that the productivity becomes low and the cost at the time of mass-production is raised. Also, the prior art wheel support bearing assembly represented by the one disclosed in the above mentioned publication has a problem in that since bearing component parts have a high rigidity and the strain occurring in a stationary member is low, it is difficult to detect the load acting on the vehicle wheel with high sensitivity.